Charge meter using a clock |
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This device measures charge by accumulating current measurements made at one second intervals, and moving the hands of the clock for increments of charge. There are two ranges, selected by a jumper which inserts an additional shunt resistor in parallel. The lower range of 0-125 MA moves the hands 1 minute for each 1 milliampere-hour, the high range of 0-750 MA has 5 MAH increments. It also measures voltage 0-20V. Optionally, the measurements may be recorded on a PC or my Secure Digital Writer. Each minute the current count and the voltage are output in serial comma-separated values. One use is to measure the charge put into a battery by a solar cell. The current terminals of this device, the cell and the battery are put in series. The other is to measure rechargable battery capacity. The clock was modified by removing the alarm speaker to make room to glue in a 3-pin header. Two of the pins are for the coil, removed from the circuit board, whose terminals are connected to the third pin by two equal resistors. Four wires exit through the speaker hole, the fourth being the positive battery terminal. The clock continues to run continuously from its own battery. |
| This is the front and the top of the Meter. |
| There are these accessories which were made for, or can be used with, the Charge Meter: This is the AC Current Adapter, the Solid-State Relay, and the Four AA Battery Discharge Holder. |
| This is the circuit diagram |
| Two programs have been written for this instrument. This program is used with the Secure Digital Writer. It has these pages of code: Comments, Declarations, Init, main, Pulse Coil, Transmit Data |
| The second program is for the AC current adapter, and is calibrated for watt-hours. The ranges are selected by a switch on the adapter, whose position is sensed by the PICAXE. The 1 amp range moves the clock one "second" for 1 watt-minute, the 10 amp for 10 watt-minutes. It has these pages of code: Comments, Init, main, Pulse Coil, |